Nadir refers to the point directly beneath a satellite as it orbits the Earth. This is the point on the Earth's surface that is closest to the satellite at any given moment.
When a satellite is in a stable orbit around the Earth, it follows a predictable path as it circles the planet. The nadir point changes constantly as the satellite moves, but at any given moment, the nadir point is the location on the Earth's surface directly below the satellite.
Nadir is an important concept in satellite mapping and remote sensing, because it determines the angle at which the satellite captures images of the Earth's surface. If a satellite is directly over the nadir point, it is said to be in a "nadir view" or a "nadir position," which provides the most accurate and detailed view of the Earth's surface directly beneath it. However, as the satellite moves away from the nadir point, the angle of view changes, and the image becomes distorted.
For example, imagine a satellite in orbit over the United States. As the satellite moves over the Midwest, the nadir point will be somewhere over the central part of the country. If the satellite is capturing images of a specific location, such as a city or a natural feature, it will need to be in a nadir view in order to capture the most accurate and detailed image possible.
In summary, nadir is the point directly beneath a satellite as it orbits the Earth, and is an important concept in satellite mapping and remote sensing. Understanding the nadir point is essential for capturing accurate and detailed images of the Earth's surface.